Emissions control devices (e.g. catalysts, such as three-way catalysts or diesel oxidation catalysts) for treating the exhaust gas of an internal combustion engine in both mobile and stationary applications typically include a substrate (e.g. a honeycomb monolith substrate) coated with a liquid that comprises a catalyst component. Problems can arise during the coating process that can depend on the properties of the substrate that is to be coated (e.g. size of the channels, the material from which the substrate is made and its porosity) and the properties (e.g. rheology) of the liquid that is used to form the coating. Various methods and apparatus have been developed by manufacturers of emissions control devices to address these problems.
WO 99/47260 describes a method of coating a monolithic support comprising the steps of (a) locating a containment means on top of a support, (b) dosing a pre-determined quantity of a liquid component into said containment means, either in the order (a) then (b) or (b) then (a), and (c) by applying pressure or vacuum, drawing said liquid component into at least a portion of the support, and retaining substantially all of said quantity within the support.
WO 2011/080525 describes a method of coating a honeycomb monolith substrate comprising a plurality of channels with a liquid comprising a catalyst component, which method comprises the steps of: (i) holding a honeycomb monolith substrate substantially vertically; (ii) introducing a pre-determined volume of the liquid into the substrate via open ends of the channels at a lower end of the substrate; (iii) sealingly retaining the introduced liquid within the substrate; (iv) inverting the substrate containing the retained liquid; and (v) applying a vacuum to open ends of the channels of the substrate at the inverted, lower end of the substrate to draw the liquid along the channels of the substrate.